Re: [PATCH 1/2] arm64: Add enable/disable d-cache support for purgatory

[Mark Rutland <mark.rutland@arm.com>]

Hi,

On Wed, Dec 14, 2016 at 05:51:05PM +0530, Pratyush Anand wrote:
> 
> On Wednesday 14 December 2016 05:07 PM, Mark Rutland wrote:
> >I see in an earlier message that the need for sha256 was being discussed
> >in another thread. Do either of you happen to have a pointer to that.
> 
> patch 0/2 of this series.

AFAICT, that just says the the existing sha256 check is slow, not *why*
a sha256 check of some description is necessary. I'm still at a loss as
to why it is considered necessary, rather than being a debugging aid or
sanity check.

> >To me, it seems like it doesn't come with much benefit for the kdump
> >case given that's best-effort anyway, and as above the verification code
> >could have been be corrupted. In the non-kdump case it's not strictly
> >necessary and seems like a debugging aid rather than a necessary piece
> >of functionality -- if that's the case, a 20 second delay isn't the end
> >of the world...
> 
> Even for the non-kdump ie `kexec -l` case we do not have a
> functionality to bypass sha verification in kexec-tools. --lite
> option with the kexec-tools was discouraged and not accepted.

Ok. Do you have a pointer to the thread regarding that, for context?

> So,it is 20s for both `kexec -l` and `kexec -p`.

Well, unless we can have a --{no-,}sha-check, and make the default NO
for arm64.

> Also other arch like x86_64 takes negligible time in sha verification.

That's certainly an argument for not changing the other architectures,
but given it's slow for arm64, we could have a different default...

Thanks,
Mark.

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